Carbyne – the evolution of Carbon NanoTube CNT

Figure – Bending stiffness of carbyne. (a) The carbon ring model with its electron density distribution, showing the usual bond alternation pattern. (b) The energy as a function of ring curvature calculations used to extract the bending modulus value.

 

 

Figure – The evolution of highest occupied molecular orbital (HOMO) in an 18-atom carbyne chain with =CH2 end-group handles under torsion. Green and red represent the opposite signs of the orbital

 

We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne’s mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5*10^{7} Nm/kg, requiring a force of ~10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be `switched on’ by appropriate functional groups at the ends. We reconstruct the equivalent continuum-elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g. a Young’s modulus of 32.7 TPa with an effective mechanical thickness of 0.772 {\AA}). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 3.2 to 4.4 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable, and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne-carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).

 

Source: http://arxiv.org/abs/1308.2258

PDF http://arxiv.org/pdf/1308.2258v1

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